Phantom Fish
A small pond lies under the Opéra Garnier, the old opera house, in addition to the Métro. Created during construction in the 1860s to contain water that flooded the foundation pit, the pond is inhabited by large fish, which are fed by opera employees.]]>

Deceptive Display
Behind the neat stacks of skulls, tibias, and femurs in the Paris catacombs lies a chaos of bones. In the 18th and 19th centuries the city dug up millions of skeletons from over-flowing cemeteries and poured them at night into old quarries.]]>

Pillars of Paris
In 1710 workers digging tombs below Notre Dame found the blocks of a more decorative pillar erected 17 centuries earlier by Seine boatmen in what was then Gallo-Roman Lutetia. Displayed now in the Cluny Museum, the find was the first evidence linking names to images of Gallic gods such as Cernunnos, shown here, whose horns likely symbolized male fertility. "It's something like the Rosetta stone," says curator Isabelle Bardiès-Fronty.]]>

Finale
Sparks fly from a performance in front of Notre Dame, on the île de la Cité. Some of the 12th-century cathedral's limestone blocks came from quarries on the Left Bank. "The history of the quarries is a history of the city," says archaeologist Marc Viré.]]>

Way Down
Many Parisians visit the underground daily via Métro stations like the Lamarck-Caulaincourt in the 18th arrondisement. Tourists who'd like a more in-depth underground experience can sign up for a walking tour that includes a stop at a "ghost" station.]]>

Paris Gets Down
The sweat and rhythm of Saturday night fill the arched cellar of Chez Georges, in Saint-Germain-des-Prés. With limited room aboveground, many clubs and restaurants expand downward, drawing people into spaces once reserved for wine.]]>

Under the Stones
At a book party in another quarry, artist Michel Chevereau (above, wearing headlamp) and writer Jack Manini (on Chevereau's left) sign copies of their graphic novel Le Diable Vert. Set in and under Paris during the Nazi occupation, it combines history—Resistance fighters hid in the tunnels—with folktales of a subterranean green devil.]]>

The Beach
In a sandy chamber known as the "beach," a wave rolls across a wall painted (and repainted) by cataphiles in the style of Japanese printmaker Hokusai. Such works can take hundreds of hours—the painting but also the carrying in of supplies.]]>

Portal
Sunlight from a boulevard falls on firefighters practicing underwater rescues in the Canal Saint-Martin, whose construction was ordered by Napoleon in 1802. The canal runs from the Seine near the Bastille to the northern edge of Paris.]]>

Bonjour to All That
Cataphiles Yopie and Dominique head for the surface through an abandoned train tunnel after scuba diving in a flooded quarry. Like many of their peers, they love the freedom underground. "At the surface there are too many rules," Yopie says. "Here we do what we want. Where else is that possible?"]]>